The present invention relates to a multiunit tube for radiating ultraviolet light and visible light, and more specifically, to a spectrophotometer using the multiunit tube.
Spectrophotometers of the so-called pre-spectral type are conventionally known in the art. In one such spectrophotometer, as disclosed in Japanese Patent Publication No. 55-4253, light emitted from a light source is separated into its spectral components by a spectroscope, whereupon a light beam of a desired wavelength length is applied to a sample. Then, the light beam transmitted through the sample is detected by a detector. Thus, the absorbance or other properties of the sample are measured.
According to these prior art pre-spectral spectrophotometers, the light from the light source is diffracted spectrally, and the light beam of the desired wavelength is applied selectively to the sample. Thus, the measurement requires means for such selection, and therefore, it cannot be accomplished with speed. Moreover, the space around the sample must be kept dark, lest stray light interfere with the diffracted light. In consequence, the operating efficiency of the spectrophotometers is low.
In order to cope with these problems of the pre-spectral system, there have been developed multi-wavelengths spectrophotometers of the so-called post-spectral type.
According to the post-spectral spectrophotometers, the light from the light source is applied directly to the sample, and the light beam transmitted through the sample is separated into its spectral components by a spectroscope, which is formed of a holographic concave diffraction grating. The spectral components or beams, having wavelength within the range of the ultraviolet or visible spectrum, are focused on a photodetector or which a plurality of beam spots are separately formed along a straight line. The spectrally diffracted beams are detected by the photodetector, which is formed of a silicon-photodiode array, disposed on the converging point of the diffracted beams, and covering channels 64 to 1,024 of the array.
A silicon photodiode has a high sensitivity to visible light, and a low sensitivity to ultraviolet light. In the multi-wavelength spectrophotometers of the post-spectral type, therefore, stray light beams, such as scattered beams, account for a substantial percentage of all the light beams (covering all the wavelength ranges) introduced into the spectroscope. It is therefore difficult to make an effective measurement.
An improved multi-wavelength spectrophotometer of the post-spectral type has been developed. This version includes an ultraviolet light source and a visible light source, such that ultraviolet and visible light beams, emitted from the light sources, are applied alternatively to a sample, using a selector mirror for selection.
The spectrophotometer of this type, however, requires the selector mirror, shiftable for the selection between the ultraviolet and visible light beams, and a drive mechanism for the mirror. The shift of the mirror takes much time and lacks reliability.
In consideration of these circumstances, use of a multiunit tube, incorporating the ultraviolet and visible light sources as a unit, has been proposed and tried.
In FIG. 1, showing an example of the multiunit tube, numeral 2 designates a casing, the inside of which is divided into two chambers 6 and 8 by partition wall 4. Wall 4 is formed with opening 10. Deuterium lamp 12 and tungsten lamp 14 are arranged beside opening 10, in first and second chambers 6 and 8, respectively. Casing 2 is formed with window 16 on the side of first chamber 6, corresponding in position to opening 10. An ultraviolet light beam, emitted from lamp 12, and a visible light beam, emitted from lamp 14, are radiated through window 16.
In FIG. 2, full lines represent the visible- and ultraviolet-spectrum radiation characteristics of the multiunit tube constructed in this manner. As seen from FIG. 2, the luminous intensity of lamp 12 is very high in the range of the ultraviolet spectrum, and lowers drastically as the wavelength becomes longer. On the other hand, the luminous intensity of lamp 14 is very high in the range of the visible spectrum, and lowers as the wavelength becomes shorter.
As mentioned before, the sensitivity of the silicon photodiode, which is used as the detector, is high within the range of the visible spectrum, and very low for the ultraviolet spectrum, as indicated by as dashed line in FIG. 2.
As indicated by a two-dot chain line in FIG. 2, therefore, the output of the detector is high in the range of the visible spectrum, and very low in the range of the ultraviolet spectrum. Thus, ultraviolet measurements are suspectible to the influence of visible light, so that spectrophotometric operation cannot be accomplished with stability.